Abnormally high cholesterol levels (hypercholesterolemia) are strongly associated with cardiovascular disease because they promote atheroma development in arteries.
Potential hypocholesterolemic pharmaceuticals and food products are continuously being developed in order to control serum cholesterol in persons with abnormally high levels. These pharmaceuticals can be based on interruption of the enterohepatic circulation (EHC) of bile salts. Bile salt metabolism and cholesterol metabolism are closely linked. Bile salts are the water-soluble excretory end-products of cholesterol, and are essential for emulsification of fats in the digestive tract. They are synthesised in the liver mainly as glyco- or tauro-conjugates. Bile salts are secreted several times a day (six on average) in the duodenum, and pass through the jejunum into the ileum. During intestinal transit, most of the bile salts are reabsorbed to return to the liver via the portal vein. A small proportion is lost within the faeces and this loss is to be newly synthesised from endogenous cholesterol in the liver. An increase of the amount of bile salts that are lost within the faeces results in an increased neosynthesis of cholesterol, thus effectively reducing the endogenous cholesterol pool. A group of currently used hypocholesterolemic drugs named resins (Cholestyramine, Colestipol, Colesevelam) are active through this mechanism of action.
Apart from the pharmaceutical or surgical attempts to lower serum cholesterol levels through interruption of the EHC, it has been suggested that the ingestion of certain bacterial cells might also influence cholesterol levels. Intestinal bacteria can influence cholesterol levels through assimilation of exogenous cholesterol from the diet in the bacterial membrane or through bile salt deconjugation. During intestinal transit, bile salts undergo a number of bacterial transformations of which one of the most important is bile salt deconjugation. The ability to deconjugate (or hydrolyse) bile salts is encountered in some intestinal lactic acid bacteria (LAB) species, but also in other genera. Upon bile salt deconjugation, glycine or taurine is liberated from the steroid moiety of the molecule, resulting in the formation of free (deconjugated) bile salts. Free bile salts are more easily precipitated at low pH. They are also less efficiently reabsorbed than their conjugated counterparts. Hence, deconjugated bile salts are more readily excreted within the faeces that conjugated bile salts. Bile salt deconjugation influences the EHC by increasing the excretion of bile salts and is believed to be much more effective in the reduction of blood cholesterol levels than the mere retention of exogenous cholesterol.
Bile salt hydrolase (BSH), the enzyme responsible for bile salt deconjugation during EHC, has been detected in several LAB species indigenous to the gastrointestinal tract. Tanaka et al. (cf. “Screening of Lactic Acid Bacteria for Bile Salt Hydrolase Activity”, Journal of Dairy Science 1999, vol. 82, p. 2530-35) screened more than 300 strains of LAB from the genera Bifidobacterium and Lactobacillus and the species Lactococcus lactis, Leuconostoc mesenteroides, and Streptococcus thermophilus. Results obtained for 273 strains showed that BSH activity is heterogeneously distributed among the different species. According to this study, nearly all bifidobacterial strains have BSH activity, whereas this activity can only be found in selected strains of lactobacilli.
Lactobacillus plantarum is a Gram-positive aerotolerant LAB commonly found in many fermented food products as well as anaerobic plant matter. It is also present in saliva (from which it was first isolated). L. plantarum strains are especially suitable for the industrial preparation of fermented food products thanks to their good survival rate through the industrial process and conservation period, as well as their high acidification profile and good organoleptic properties. Some strains of L. plantarum are also considered as probiotics. Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host. To be termed as probiotic, the bacteria must fulfil several requirements related to their lack of toxicity, viability in reaching the lower gastrointestinal tract (GIT) and adhesion to the intestinal mucosa, among others. Most probiotic bacteria belong the LAB group but, nevertheless, it is generally known that probiotic features and benefits are extremely strain-dependent, even among LAB of the same species.
The commercial L. plantarum 299v strain is generally regarded as probiotic and has been described to decrease the fibrinogen and cholesterol levels in serum when ingested in the form of a probiotic drink (cf. Bukowska et al., “Decrease in fibrinogen and LDL-cholesterol levels upon supplementation of diet with Lactobacillus plantarum in subjects with moderately elevated cholesterol” Atherosclerosis 1998, vol. 137, p. 437-38). However, LDL-cholesterol reduction was very moderate in these studies and was accompanied by a similar mild reduction of HDL-cholesterol. No data related to BSHA of L. plantarum 299v has been published.
It is therefore desirable to provide new improved probiotic strains to be used as hypocholesterolemic agents.